1. Field of the Invention
The present invention relates to a sheet post-processing apparatus that carries out post-processing on a sheet bundle and a control method therefor, and in particular to a sheet post-processing apparatus for carrying out a stapling process on a sheet bundle.
2. Description of the Related Art
In general, after image formation on sheets (printing) is carried out, two or more sheets are bundled, and an end of the sheet bundle is stapled (stitched) at one or a plurality of positions. Further, so-called saddle stitching may be carried out in which a sheet bundle is stitched in a central part thereof in a conveying direction and then folded in two in the stitched part. Also, so-called side stitching in which an end of a sheet bundle is stitched may be carried out. To carry out such a stapling process, a so-called sheet post-processing apparatus is used.
In the stapling process described above, a stapler drives a metallic staple through a sheet bundle to staple the sheet bundle. However, there may be cases where a staple is not driven through a sheet bundle for some reason. When a sheet bundle through which a staple has not been driven is discharged from the sheet post-processing apparatus, a user needs to manually staple the sheet bundle. As a result, post-processing efficiency significantly decreases.
To address such a problem, for example, a metallic sensor (staple presence-absence sensor) is provided in a sheet conveying path so that the metallic sensor detects whether or not a staple has been driven through a sheet bundle (see Japanese Laid-Open Patent Publication (Kokai) No. 2005-263441).
According to Japanese Laid-Open Patent Publication (Kokai) No. 2005-263441, however, whether or not there is a staple in a sheet bundle is merely detected, and no consideration is given to how a staple can be accurately put at a predetermined stapling position after a stapling process.
In particular, when a user operates a stapler in, for example, exchanging staples, the position of the stapler may slightly change. As a result, for example, a folding position and a position of a staple in saddle stitching may be out of alignment, and a bound book may be poor-looking.